unit 7 physiology - digestive system

kidneys & the urinary system

kidney functions

• regulating water balance, salt concentration, and pH balance

• influencing red blood cell production and blood pressure

• filtering toxic substances out of your blood for removal from the body

go look at nephrons

glomerular filtration rate (GFR)

= how much blood passes through the glomeruli every minute

• changes as blood pressure changes (if blood pressure rises, the filtratoin rate will decrease)

• too much stuff going in too fast = bad for filtration

endocrine regulation

ADH → water retention

• hypothalamus detects the drop in blood plasma water levels and higher relative NaCl levels

• ADH is released, which causes more aquaporins to open in the collecting duct → increased water resorption

aldosterone → increased blood pressure

aldosterone secreted by the adrenal gland increases Na+ resorption in the distal convoluted tubule.

increased blood plasma NaCl levels → hypothalamus detects change → ADH release = water retention → increased blood volume → increased blood pressure

nutrient absorption

chemical digestion

mouth

salivary feedback

• tastes good = more saliva produced, perceives food more readily

• tastes bad = less saliva produced

• starch —(amylase)→ glucose

stomach (& gastric pits) - goblet cells

• goblet cells = produce mucus

stomach (& gastric pits) - chief cells

chief cells

• make gastric lipase (lipid digestion)

• make pepsinogen

• deals with lipids and proteins

stomach (& gastric pits) - parietal cells

parietal cells

• make intrinsic factor for vitamin B12 absorption

• make HCl

pepsinogen & pepsin

pepsinogen —HCl→ pepsin = breaks down proteins in food

pepsinogen has additional peptides on it, HCl removes peptides, then it is pepsin

liver and pancreas

• liver produces bile all the time

• duodenum produces hormone CCK (cholecystokinin) in response to food consumption (fats in particular)

• CCK causes gall bladder to contract to release the bile

• CCK causes the pancreas to make digestive enzymes for digestion

CCK

cholecystokinin

• produced in response to food consumption (fats in particular)

• CCK causes gall bladder to contract to release the bile

• CCK causes the pancreas to make digestive enzymes for digestion

small intestine

• lacteal = lymphatic vessel

• chylomicrons = protein coats that surround emulsified fats before they are absorbed by lacteals

• carbs and amino acids are absorbed by capillaries → hepatic portal vein system

lacteal

lymphatic vessel

chylomicrons

protein coats that surround emulsified fats before they are absorbed by lacteals

large intestine

• 500ml of food → 150mL of feces (on average)

• 90% of water absorption occurs in large intestine

  • fiber in diet stops the intestine from squeezing itself (painful)

• farts = caused mostly by gut microbiome bacteria

  • bacteria digest material that is left over (primarily plant fiber carbohydrates) and release CO2 & CH4

peristalsis

moves digested material towards rectum

brain cell

• can burn glucose and ketone bodies

• prefers to burn glucose

• cannot store molecules

• can convert one type of fuel molecule to another

• doesn’t generally send fuel molecules to other cells

fat cells

• can burn glucose and fatty acids

• prefers to burn fatty acids

• stores large amount of energy as fat molecules

• can convert one type of fuel to another

• sends fuel molecules to other cells

muscle cells

• can burn glucose and fatty acids

• prefers to burn fatty acids

• stores glycogen

• doesn’t convert one type of fuel molecule to another

• sends fuel molecules to other cells

red blood cells

• can burn glucose

• prefers to burn glucose

• stores hemoglobin?

• can convert one type of fuel molecule to another

• sends precursor to liver, doesn’t send full fuel molecules to other cells

liver cells

• can burn any nutrient

• prefers to burn fatty acids

• stores glycogen and fats

• can convert one type of fuel molecule to another

• sends fuel molecules to other cells

lipids

breakdown: Lipid breakdown involves the mechanical churning of the stomach and the emulsifying action of bile in the small intestine, which allows pancreatic lipase to chemically cleave large triglycerides into absorbable free fatty acids and monoglycerides.

absorption: Lipid absorption occurs when micelles ferry digested fats to the intestinal wall for diffusion into cells, where long-chain fats are reassembled into triglycerides and packaged into chylomicrons to be transported through the lymphatic system into the blood.

proteins

breakdown: Protein breakdown begins with stomach acid denaturing the protein's shape so that pepsin and pancreatic proteases (like trypsin) can chemically cleave the long chains into smaller peptides and individual amino acids.

absorption: Protein absorption involves specialized transport proteins actively pumping amino acids and small peptides into the intestinal cells, where they are released directly into the bloodstream to be carried to the liver for distribution.

carbs

breakdown: Carbohydrate breakdown starts with salivary amylase in the mouth and continues in the small intestine where pancreatic amylase and brush border enzymes (like maltase and sucrase) finish cleaving complex starches and disaccharides into simple monosaccharides like glucose.

absorption: arbohydrate absorption occurs as monosaccharides are moved into intestinal cells via active transport or facilitated diffusion and then released directly into the bloodstream to be transported to the liver for immediate energy use or storage.

nucleic acids

breakdown: Nucleic acid breakdown begins in the small intestine where pancreatic nucleases break down DNA and RNA into nucleotides, which are then further cleaved by brush border enzymes (nucleosidases and phosphatases) into their basic components: nitrogenous bases, pentose sugars, and phosphate ions

absorption: Nucleic acid absorption involves the use of active transport carriers to move the resulting sugars, bases, and phosphates across the intestinal lining and into the bloodstream, where they are transported to the liver and other tissues for reuse in cellular processes.

next: white board the digestive tract diagram and label, white board the nephron process and MEMORIZE!, study these more.